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LINKS2HEALTHIERBUBS: A DATA LINKAGE STUDY ESTIMATING THE EFFECTIVENESS OF MATERNAL PERTUSSIS VACCINATION AMONG AUSTRALIAN INFANTS
Abstract
Background
Maternal immunisation is a recommended strategy for protecting young infants from pertussis-related morbidity and mortality. Between 2014-2015, Australian jurisdictions introduced and funded diphtheria-tetanus-acellular pertussis (dTpa) vaccination programs for women from 28 weeks of pregnancy.
Aims
We aimed to estimate the effectiveness of maternal pertussis immunisation overall and by gestational age at dTpa vaccination.
Methods
We established a population-based cohort of mother-infant pairs between 2014 and 2017 using probabilistic linkage of three Australian jurisdictional data collections: Western Australia, Northern Territory and Queensland. Jurisdictional immunisation records were used to define maternal vaccination status; notification records were used to identify pertussis infections in infants from 0-6 months of age. Risk ratios (RR) were estimated using log-binomial regression weighted by inverse probability of vaccination. We estimated vaccine effectiveness (VE) as 1-RR overall and by gestational age at vaccination.
Results
Among 294,342 mother-infant pairs, 51.5% received dTpa vaccination during pregnancy, predominantly between 28–31 weeks of pregnancy. VE was 74% (95% CI 54%, 86%) among <2 month olds, 64% (95% CI 31%, 81%) in 3–4 month olds, and 60% (95% CI 28%, 77%) in 5–6 month olds. We observed similar estimates of VE for pregnancies immunized prior to 28 weeks (VE: 72% 95% CI 37%, 88%) and pregnancies immunized at 32 weeks or later (VE 68%; 95% CI 40%, 83%).
Conclusions
Results support current policies recommending dTpa vaccination during pregnancy and indicate vaccination is effective when administered prior to 28 weeks of gestation. Pertussis immunisation during pregnancy could prevent a majority of pertussis cases in infants <6 months of age.